Investigation of near wall velocity in 3-D smooth channel flows

This paper presents an investigation of velocity distribution in steady, uniform flows in smooth rectangular channels. Theoretical study and experimental data show that the near wall velocity distribution in 3-D channels cannot be represented well by the classical log-law where the shear velocities are identical on both sides of the equation (Tracy and Lester, US Department of Interior, Washington, DC, 1961, pp. A1-A18). This paper examines the appropriate expressions of two shear velocities that may be different. In the light of Tracy and Lester's work, this study found that when the measured near wall velocity and wall normal distance are normalized by the global shear velocity and the local shear velocity, then the near wall velocity can be described by the well-known wall function without an empirical coefficient. The basic mechanism is attributed to the concept proposed by Yang and Lim [J. Hydraul. Engng. ASCE 123 (1997) 684] that surplus mechanical energy is transported towards boundary along shortest path. The derived equations are in good agreement with experimental data in the literature.